Rapid quantitative determination by ~(13)C NMR of the composition of acetylglycerol mixtures as byproduct in biodiesel synthesis

摘要

Commercially available partly acetylated glycerols (mono- and diacetin) are mixtures of glycerol, 1- and 2-acetylglycerol, 1,2- and 1,3-diacetylglycerol, and triacetin. Diacetin and monoacetin are by-products of the biodiesel and triacetin production using glycerol esterification with acetic acid or triglyceride inter-esterification with methyl acetate. Usually, primary analytical methods involve chromatography (HPLC or GC), spectroscopy (MS or NIR), and wet chemical techniques (potentiometric, iodometric titration) which are often time-consuming due to sample preparation, extended analysis time and/or complicated data analysis. Moreover, these methods require pure mono- and diacetin as standard, which are commercially unavailable. In this work, a complete ~(31)P and ~(13)C chemical shift data for glycerol, mono-, di- and triacetin (including isomers) allows for the identification and quantification of these components in the commercial mixtures. This experimental protocol allows for rapid analysis of mixtures that include these six components. Quantitative ~(31)P NMR and ~(13)C NMR results were validated to those obtained with other analytical methods, such as GC and HPLC-ELSD. ~(13)C NMR is preferred due to allows to measure the content of triacetin, which has no free hydroxyl group, and no signal was detected by ~(31)P NMR.